1. Field of the Invention
The present invention relates to a display device, and more particularly, to a liquid crystal display device and a method for manufacturing the same. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for preventing a touch failure on the display screen of the liquid crystal display device.
2. Discussion of the Related Art
As the information age has developed, the need for a flat panel display device has increased. To meet this need, various types of flat panel display devices, such as a liquid crystal display (LCD), a plasma display panel (PDP), an electro luminescent display (ELD), and a vacuum fluorescent display (VFD), have been developed. Such flat panel display devices are used as display devices in different types of apparatuses.
Recently, the LCD is the flat panel display that has been replacing the cathode ray tube (CRT) because the LCD has lighter weight, thinner profile, and lower power consumption than the CRT. Further, the CRT is used for various other display purposes, such as a monitor of a notebook computer. To use the LCD as an image display device in a variety of fields, it is important to maintain the advantageous characteristics of the LCD, such as light weight, thin profile, and low power consumption as well as a high-quality image having high definition and high luminance.
In general, a liquid crystal display device includes a first substrate and a second substrate, which are bonded to each other with a gap therebetween, and a liquid crystal display layer injected into the space between the first substrate and the second substrate. A plurality of gate lines are disposed at regular intervals in a first direction and a plurality of data lines are disposed at regular intervals in a second direction perpendicular to the first direction on the first substrate. The data lines and the gate lines cross each other and define pixel regions. Pixel electrodes are respectively formed in the pixel regions, and TFTs are formed at the crossings of the gate lines and the data lines in the pixel regions to apply data signals from the data lines to the pixel electrodes in response to signals applied to the gate lines.
A black matrix layer for blocking light is formed on the second substrate. Red, green, and blue color filter layers are formed in the black matrix corresponding to the pixel regions for forming colors. The black matrix layer blocks light except at the portions corresponding to the Red, Green, and Blue color filter layers. A common electrode is form on the color filter layers for forming an image together with the pixel electrode.
In the liquid crystal display device described above, the liquid crystal molecules of the liquid crystal layer between the first and second substrates is oriented by an electric field formed between the pixel electrodes and the common electrode such that the amount of light penetrating through the liquid crystal layer is controlled according to the orientation degree of the liquid crystal molecules. Such a liquid crystal display device is referred to as a twisted nematic (TN) mode liquid crystal display device. The TN mode liquid crystal display device has a narrow viewing angle. To solve the drawback of a narrow viewing angle in the TN mode liquid crystal display device, an in-plane switching (IPS) mode liquid crystal display device has been developed.
In the IPS mode liquid crystal display device, parallel pixel electrodes and common electrodes, which are separated from each other by a designated interval, are both formed on the first substrate in the pixel regions so that a horizontal electric field is generated between the pixel and common electrodes, and the liquid crystal molecules of the liquid crystal layer are oriented by the horizontal electric field.
Spacers for maintaining a gap for the liquid crystal layer are provided between the first and second substrates in both the IPS mode and TN mode LCD devices. The spacers can either be ball spacers or column spacers. The ball spacers have a spherical shape, and are scattered in between the first and second substrates such that they move relatively freely about even after the first and second substrates are bonded to each other, and have a small contact area with the first and second substrates. The column spacers have a column shape at a designated height that are formed during fabrication of one of the first and second substrates, and are affixed to one of the first and second substrates. In contrast to the ball spacers, the column spacers have large contact areas with the first and second substrates.
FIG. 1 is a cross-sectional view of the related art liquid crystal display device having column spacers. As shown in FIG. 1, the liquid crystal display device 10 includes a first substrate 30 and a second substrate 40, which face each other, column spacers 20 formed between the first and second substrates 30 and 40, and a liquid crystal layer (not shown) filling a gap between the first and second substrates 30 and 40. Gate lines 31 and data lines (not shown) perpendicularly cross each other on the first substrate 30 to define pixel regions (not shown). TFTs (not shown) are formed at crossings of the gate lines 31 and the data lines in the pixel regions, and pixel electrodes (not shown) are formed in the pixel regions. Further, a gate insulating film 36 is formed over the surface of the first substrate 30, including the gate lines 31, and a passivation film 37 is formed on the gate insulating film 36.
A black matrix layer 41 for blocking light is formed on the second substrate 40. A stripe-shaped color filter layer 42 corresponding to the pixel regions and having color filters arranged in a longitudinal direction parallel with the data lines formed on the black matrix layer 41. A common electrode or an overcoat layer 43 is formed on the stripe-shaped color filter layer 42 of the second substrate 40. The column spacers 20 are formed at designated positions above the gate lines 31.
FIGS. 2A and 2B are respective plan and cross-sectional views of a touch failure of a related art liquid crystal display device having column spacers. As shown in FIGS. 2A and 2B, when the surface of the above related art liquid crystal display device 10 is touched by a hand or other objects in a designated direction, a defect in the display of the liquid crystal display device 10 is generated at the touched region. This type of display defect is referred to as a touch stain or touch failure.
The column spacers 20 have a large contact area between the column spacers 20 and the first substrate 1 as compared to a liquid crystal display device having ball spacers. The large contact area increases frictional force therebetween such that a touch failure. That is, compared to the ball spacers, since the column spacers 20 having cylindrical shapes as shown in FIG. 2B, have a large contact area with the first substrate 1, it takes a long time to return the first or second substrate 1 or 2 to its original state after the first or second substrate 1 or 2 is shifted, and a stain remains for a long time.
The related art liquid crystal display device having column spacers has several problems. A contact area between the column spacers and the substrate opposite thereto is large, thus increasing friction between the column spacers and the opposite substrate. When the liquid crystal display device is touched such that one of the substrates is shifted, it takes a long time for the shifted substrate to return to its original state because of the friction, and thus a stain can remain indefinitely. Further, when the liquid crystal display device having the column spacers is stood upright in a high-temperature environment, the liquid crystal can thermally expand the cell gap to a height larger than the column spacers such that the liquid crystal flows down toward the lower end of the liquid crystal display device so as to cause a swollen opaque area.